1. Field of the Invention
The present invention is directed to a diamond heat sink having an excellent heat release characteristics, which incorporates a thermistor or a cooling element with higher thermal response, and is also directed to a method of manufacturing it.
2. Related Background Art
Diamond is a suitable material for heat sink, because diamond has excellent thermal conductivity of more than 2,000[W/m.multidot.K]. Further, since diamond can acquire the characteristic of semiconductor material when impurities are doped into the diamond, the resultant doped diamond can be employed as a thermistor material which has an capabilities for the use at elevated temperature and has a quick thermal response characteristics.
Japanese Patent Laid-open No. 63-184304 discloses a thermistor made with diamond. A semiconductor diamond film is formed on a substrate by vapor phase synthesis. The semiconductor diamond film of this reference serves as a heat sensitive film. Ohmic electrodes are formed on the heat sensitive film. The resistivity of the heat sensitive film are measured through these Ohmic electrodes to determine the temperature of the heat sensitive film. Examples of the available substrates on which the heat sensitive film is formed include single crystal diamond substrate, metal having a high melting point and a high thermal conductivity, semiconductor, and other compound(s) thereof.
In Japanese Patent Laid-open No. 5-67711 discloses a thermistor made of diamond to be integrated with a heat sink made of diamond, and the manufacturing method of the thermistor-integrated heat sink. According to the construction of the thermistor with this manner, the semiconductor diamond film as the heat sensitive film is formed on a predetermined region of a heat sink material by the vapor phase synthesis, and metal electrodes are then formed on the heat sensitive film. A metallized film is also formed on the surface of the heat sink material next to the thermistor. The exothermal elements such as diode and FET are seated onto the metallized film for their temperature to be measured. The exotherms from the element on the metallized film is conducted to the thermistor through the heat sink material, and the temperature of the element can be measured. Japanese Patent Laid-open No. 5-67711 also shows another thermistor-integrated heat sink. The semiconductor diamond film as the heat sensitive film is formed on the entire surface of the heat sink material and metal electrodes are formed onto the heat sensitive film. A metallized film is formed onto the surface of the heat sensitive film between the metal electrodes, and the exothermal elements are seated onto the metallized film. In both of the thermistor-integrated heat sinks of the Japanese Patent Laid-open No. 5-67711, single crystal diamond, metals having high melting point and higher thermal conductivity (or refractory metals with higher thermal conductivity), semiconductor or other compound(s) thereof are used for the heat sink material.
As mentioned above, in Japanese Patents Laid-open Nos. 63-184304 and 5-67711, the single crystal diamonds are employed as the substrate of the thermistor of the former and as the heat sink material of the thermistor-integrated heat sink of the latter, respectively. Single crystal diamonds of a consistent quality can be obtained through artificial synthetic method under extra high pressure, which are still costly.
When the vapor phase synthesis is applied to obtain the diamond heat sink, a thicker diamond would be required for the substrate and the heat sink, because of insufficient performances of the diamonds made via vapor phase synthesis. Further, since the vapor phase synthetic diamond is polycrystalline, the surface of the diamond would be considerably rough. Thus, the rough surface of the synthetic diamond needs to be polished and made flat to mount the exothermal elements. However, since diamond is an extremely hard material, the polishing process for synthetic diamond includes significant difficulties.
In the heat sink construction of Japanese Patent Laid-open No. 5-67711 where the thermistor and the exothermal element are arranged in parallel on the heat sink material, the exotherms from the exothermal element is transferred through heat sink material to the thermistor. Thus, the heat would be detected with some delay, and some of the heat would be absorbed by the heat sink material in the heat transfer process from the exothermal element to the thermistor. Therefore, the thermistor-integrated heat sinks of the above references have insufficient abilities to precisely detect and control a temperature of the mounted exothermal element.
U.S. Pat. No. 5,022,928 discloses a film-shaped thermoelectric heat pump of the Peltier element type in which Bi.sub.2 Te.sub.2 etc. are laminated onto a substrate. This patent, however, not directed to the improvement of heat transfer. In addition, the patent does not describe the point of quick response required when it is used as a heat sink.
Consequently, it is desirable to present a heat sink with a quick response which comprises a synthetic diamond made via a vapor phase synthesis.